Preheat your oven to 375°F (190°C).
In a large skillet, heat oil over medium heat. Add ground beef, diced onion, and minced garlic. Cook until browned, about 7-10 minutes. Drain excess fat.
Stir in taco seasoning, black beans, corn, and diced tomatoes. Cook for an additional 5 minutes. Season with salt and pepper.
Grease a 9x13 inch baking dish. Spread the beef mixture evenly, spoon dollops of sour cream, and sprinkle cheeses on top.
Arrange frozen tater tots in a single layer over the cheese. Bake for 30-35 minutes until golden brown and crispy. Let cool for 5 minutes before serving.